THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 265 
General Conclusions. 
In the dog, cat, rabbit (and in so far as the writer’s 
experiments go, in the rat and the mouse) neither the 
brain cortex nor the underlying white matter is ex- 
citable by electrical stimulation at birth or for some 
days afterwards. 
The cortex is usually not excitable till about the period 
when the eyes open, though there are exceptions to 
this rule, most frequent in the writer’s experience in 
the cat, in favour of an earlier date. 
The white matter of the brain, just beneath the 
cortex, is generally excitable, either at an earlier date 
than the cortex, or witha weaker stimulus. 
The reaction for the limb movements is obtainable 
invariably somewhat earlier in the dog and the cat, 
and generally so in the rabbit, than those for the 
neck, face, ete. 
Localisation for the cortex, and still more for the 
white matter, is at first ill-defined, but gradually, 
though rapidly, becomes more definite. 
In the cavy (guinea-pig) the cortex and the white 
matter beneath are electrically excitable either at birth 
or a few hours afterwards, and perfection of reaction 
and localisation is reached in a few days. 
Before the brain cortex responds to electrical ex- 
citation, ablation of the motor area (centres) leads to no 
appreciable interference with movements. 
The younger the animal, the stronger the current 
required to produce reaction up to the time that localisa- 
tion is well established, 7.e. the weakness of the current 
required to cause a movement is an indication of the 
degree of development of the centre in question. 
Differences for breeds and individuals exist and 
